1. Field of the Invention
The present invention relates to an improved coal gasification method of the type using coal powder.
In veiw of recent circumstances relating to an energy problem, the utilization of coal energy is again in the limelight.
To meet the demand of suppliers and users which have been accustomed to the handy form of the conventionally used energy sources such as petroleum and gases, it has been considered as an urgent necessity to study and solve the problems of coal liquefaction and gasification and many proposals have been made for these purposes. The conventional coal gasification techniques include fixed-bed type fluidized bed methods, jet stream methods and others, and the technique of the present invention comes within the category of the fluidized bed methods. More specifically, the invention is directed to a method in which the reaction temperature region of a fluidized bed is maintained at around 1,100.degree. C. so that an agglomerated bed of fluidized material is formed and thus the gasification furnace capacity and the coal gasification quantity are increased.
2. Description of the Prior Art
U.S. Pat. No. 3,454,383 discloses a fluidized bed type coal gasification method and apparatus of the above type. In the method and apparatus of this patent, coal having a size of 1/4 to 3/8 inches, including those greater than 100-mesh size, is fed into the neck portion of a vertical gasification furnace having a cooling coil around its outer surface and lined with a refractory material, along with its product gas which will be described later. Also, air and sieved pulverized coal of smaller than 100-mesh size are fed into a cyclone furnace along with the gas produced thereby which will be described later and they are then blown by the cyclone furnace into the furnace chamber so as to be burned therein at a combustion temperature of 3,000.degree. F. (1650.degree. C.) and thereby to form a gasification zone as a fluidized bed in the part above the neck portion. The resulting gas and products are introduced into a heat exchanger annexed to the gasification furnace and their sensible heat of 1,800.degree. F. (980.degree. C.) is subjected to heat exchange. The gas and products are then introduced into a dust collector so that the separated char is fed back to the cyclone furnace and a portion of the product gas is also fed back to the combustion system.
However, the above-mentioned known method and apparatus are disadvantageous in that the reaction temperature is low due to the ordinary fluidized bed type and the reaction time is also long due to the coarse and large particle size of the coals.
Known jet-type coal gasification methods includes the Koppers-Totzek method. This method is disadvantageous in that coal must be pulverized so that more than 80% passes through a 200-mesh screen with the resulting increase in cost and that with the furnaces according to the method the rate of gasification (the rate of gasification of coal to reducing gases such as Co and H.sub.2 and oxidizing gases such as Co.sub.2, etc.,) is as low as about 90%. These defects are attributable to the fact that in order to prevent the fusion of ash to that part of the apparatus serving the purpose of delivering the product gas, the ash amounting to 50 to 90% of the products must be discharged in entrainment with the gas and this results in the formation of unburned carbon.
As a result, when considering any coal gasification method and apparatus, it is desirable that a gas conversion ratio of 95 to 100% is ensured.